Milling machine



Jan. l5, 1946. J. B. ARMn-AGE ETAL 2,392,953-

MILLING MACHINE Filed Jan. 6, 1941 l0 Sheets-Sheet 3 /l f INVENToRs.-

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Jan. 15, i946. J. B. ARMITAGE ET AL I 2,392,953

MILLING MACHINE Filed Jan. e, 19451 1o sheets-sheet 5 I I I l I) A TTORNEY.

Jan. l5, 1946. J. B. ARMITAGE ETAL. 2,392,963

MILLING MACHINE Filed Jan. e, 1941 1o seetsfsheet 6 l f 283 2M ZI 6 INVENToRs:

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A MILLING MACHINE Filed Jan. 6, 1941 10 Sheets-Sheet 7 ATTORNEY;

Jan. l5, 1946. J. Pla. ARMITAGE ETAL MILLING MACHINE Filed Jan. 6, 1941 10 Sheets-Sheet 8 W ZM Jan. 15,1946.

J. B. ARNm-AGE ETAL 2,392,963

MILLINGv MACHINE 10 Sheets-Sheet 9 ymd Jan. s, 1941 IIl lllllllll Il llll M m m m Jan. l5, i946. I J. ARMITAGE ET AL 2,392,963

MILLING MACHINE Filed Jan. 6, 1941 10 Sheets-Sheet 10 W, www

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Patented Jan. 15, 1946 MILLING MACHINE Joseph B. Armitage, Wauwatosa, and Harold L. Heywood, West Allis, Wis., assignors to Kearney & Trecker Corporation, West Allis, Wis., a corporation of Wisconsin Application January 6, 1941, Serial No. 373,274

9 Claims.

This invention relates generally to milling machines and more particularly to improved actuating and controlling mechanism for a machine especially adapted to mill surfaces in positions diicult of access.

The present specification constitutes a continuation in part of application Serial No. 115,650, led December 14, 1936, now Patent No. 2,227,620, dated January 7, 1941.

A general object of the invention is to provide a milling machine that is capable of performing milling operations in restricted spaces and that is adjustable to effect either curved or linear cutting strokes or a combination of both.

Another object of the invention is to provide a milling machine especially suitable for operating on Work pieces presenting restricted cavities within which milling operations are to be performed.

Another object of the invention is to provide a milling machine for operating in restricted spaces that is provided with an interlocking control mechanism arranged to effect feeding movement of a cutter relative to a workpiece through a predetermined path and to so control the cutter and the workpiece as to prevent relative movement thereof in directions which might result in damage to the machine.

Another object is to provide a milling machine driving mechanism arranged to move a milling cutter selectively through either an arcuate or a linear cutting path.

Another object is to provide an improved feeding and reversing mechanism for moving a supporting element of a milling machine.

A further object is to provide an improved hydraulically operated control system for regulating and coordinating the movements of various elements of a milling machine.

A still further object is to provide an improved hydraulically operated work-feeding mechanism for a milling machine.

According to this invention, a milling machine of the type adapted to perform milling operations in close quarters is equipped with improved transmission and control apparatus arranged to facilitate adjustment of the mechanism and to coordinate operation of the movable elements thereof. The transmission apparatus includes mechanism for positioning and for effecting feeding movements of a plurality of milling cutters and mechanism for holding a workpiece and for moving it into cooperating relationship with the cutters. The control apparatus includes interlocking means arranged to prevent relative movement of the workpiece and the cutters in directions which might result in damage to the machine or destruction of the workpiece. The cutter actuating mechanism is provided with a reversing device having a friction clutch for each direction of operation, the clutches being disposed at opposite sides of a single direct-acting piston that may be moved in opposite directions by hydraulic pressure to engage the respective clutches. Selective means are provided for causing one of the friction clutches to effect return movement of the cutters at either feed rate or rapid traverse rate.

The foregoing and other objects of this invention, which will become more fully apparent from the following detailed description of embodiments thereof, may be achieved by the apparatus herein described by way of example in connection with the illustrations of its structural components in the accompanying drawings, in which:

Figure 1 is a view in rear elevation of a milling machine constructed in accordance with the teachings of the present invention, parts having been broken away to show a portion of the transmission mechanism and portions of the movable cutter supporting elements;

Fig. 2 is a fragmentary view in front elevation of the machine shown in Fig. l illustrating the manually operable control elements;

Fig. 3 is a View of the tool supporting and driving mechanism partly in elevation and partly in section to disclose structural features of the mechanisms;

Fig. 4 is a view taken substantially along the plane represented by the line 4 4 of Fig. 1 showing means for imparting rotary movement to the tool supporting sector and also a universally jointed shaft applicable to effect straight line movement of the cutting tool when desired;

Fig. 5 is an expanded view of a portion of the transmission mechanism including the feed rate changing and reversing mechanisms for controlling the movement of the cutter supporting spin-v dles of the machine;

Fig. 6 is a detail View in section taken along the plane represented by the line 6 6 of Fig. 3

showing the adjusting mechanism for the pivotally mounted tool driving motor;

Fig. 7 is a view in vertical section of the Workholding fixture and indexing apparatus taken substantially along the plane represented by the line 1 1 of Fig. 2;

Fig. 8 is a horizontal sectional detail View of the Work indexing apparatus taken along the plane represented by the line 8 8 in Fig. 2 showing the manually operable means for rotating the Work within the work holding fixture;

Fig. 9 is a diagrammatic view of the hydraulic transmission and control circuits for effecting coordinated operation of the. various movable parts of the milling machine;

Fig. 10 is a detail view of an element of the control mechanism taken along the plane represented by the line Ill-l in Fig. 2;

Fig. 11 is a sectional view of the control element taken along the plane represented by the line in Fig.

Fig. 12 is a view in rear elevation showing a modified form of a. milling machine constructed in accordance with the teachings of the present invention, parts having been broken away to show a portion of the transmission mechanism;

Fig. 13 is an end elevational view of the machine shown in Fig. 12;

Fig. 14 is a vertical sectional View taken substantially along the plane of the line |4|4 of Fig. 12 showing a portion of the transmission mechanism including the feed rate changing and reversing mechanism for controlling the movement of the cutter and supporting spindles of the machine; and

Fig. 15 is a diagrammatic view of the hydraulic transmission and control circuits for effecting coordinated operation of the various movable elements of the milling machine shown in Fig. 12.

The machines illustrated in the drawings as constituting apparatus disclosing embodiments o-f the several features of this invention are milling machines especially adapted for milling arcuate ball raceways, such as are required in a universal joint of the type shown in Patent No. 1,522,351, to Carl W. Weiss, although the machines are also applicable to other uses.

Referring more specifically to the drawings, and particularly to Figure l thereof, the miling machine there illustrated comprises, in general, a main frame or bed 2U having at each side an inwardly inclined way for slidably receiving cutter supporting and driving mechanisms or heads 2| and 22,'respectively, disposed to cooperate with a work supporting element constituted by a work holding fixture 23 mounted on the front of the base and vertically movable relative thereto.

As may best be seen in Fig. l, each of the cutter carrying head units includes a driving motor 26 operatively connected to drive a tool spindle 21 which carries at its upper end an end milling cutter 28 in position to operate upon a workpiece 30 held by the work-supporting element 23. As the surfaces to be machined on the workpiece 3U are disposed within cavities difficult of access and are of non-linear contour, it is necessary that the cutter-supporting apparatus be made adjustable to present each of the cutters to the work at a suitable angle and to move the cutters along predetermined paths to form the desired contoured surfaces. To this end, the cutter-supporting spindles 21 are of tapered construction to permit of operation in close proximity to each other, and each driving motor 26 and its associated spindle 21 is mounted in a unitary frame that is so supported as to be adjustable in several directions.

As may be seen in Figs. 1 and 3, the frame of each driving motor 26 is suspended at its top from a pivotal supporting pin 32 in such manner that it may be swung with its associated spindle 21 through an arc to change the angle of presentation of the cutter 28, as is indicated in Fig. 3 by the dotted outline showing the motor frame in its extreme upper position. The pivot pin 32, carrying the frame of the cutter driving motor 26 and the cutter spindle 21, is supported by a bracket or cradle 33 that is slidably mounted for movement forward or backward relative to the machine base upon a cutter-carrying slide 34, as best shown in Fig. 3. The slide 34 is mounted for movement towards or from the middle of the machine, as shown in Fig. 1, upon a pivotally mounted oscillating sector or rotary base 35. The sector 35 is rotatably supported by a pivot pin 36, shown in Fig. 3, upon a main slide or sliding base 31 that slidably engages the inclined way of the frame 20.

Movement of the cutters 28 to mill a surface of arcuate contour is accomplished by turning the sector 35 about its pivot pin 36, as seen in Fig. 3, and the position and degree of curvature of the arcuate surface is determined by the positions assumed by the various adjusting slides. For cutting a lineal surface, the segment 35 is held stationary and the cutter-supporting bracket 33 is moved in a direction from back to front of the machine along the slide 34. Chips resulting from the cutting operation, and coolant applied to the cutters fall between the cutter heads 2| and 22 into a chip basin or trough 4|, Fig. 1, formed in the main frame 20, the coolant draining through a screened opening into a coolant reservoir formed within the frame 20. The accumulated chips may be removed at intervals through an opening 43 provided for that purpose in the back wall of the machine, as shown in Fig. 1.

The power driving mechanism for moving the cutter supporting head through a cutting stroke comprises essentially a driving motor 50 that is mounted on the right side of the frame 20 shown in Fig. 1 and is directly connected to drive a feed rate changing and reversing mechanism 5| from which a main driving shaft 52 (see Figs. 1 and 5) transmits power in the desired direction and at the desired rate for moving both the cutter head 2| and the cutter head 22 simultaneously. As shown in Fig. 1, the main driving shaft 52 is connected by bevel gearing 53 to a branch drive shaft 54 associated with the right cutter head 2|, and by bevel gearing 55 to a branch drive shaft 56 that is associated with the left cutter head 22. As the driving mechanisms for each of the cutter heads are similar except for being oppositely arranged, the mechanism for the right cutter head 2| only is shown in detail as illustrative of the structure.

As shown in Fig. 1, the branch driving shaft 54 of the cutter head 2| extends into a gear box 51 at the outer side of the frame 20 and has splined connection therein with a sliding gear couplet 53. With the gear couplet 58 in its lower position as shown, power is transmitted to a gear wheel 59 meshing therewith and mounted on a cutter oscillating drive shaft 60 that is operatively connected to rotate the supporting sector 35 about its pivot pin 36. As shown in Fig. 4, the shaft 60 is j ournalled in the main slide 31 and is provided at its inner end with a bevel pinion BI that meshes with a bevel pinion 62 connected toa worm 63 also journalled in the slide 31. The worm 63 meshes with worm wheel teeth 64 on the periphery of the sector 35, the arrangement being such that when the worm 63 is rotated by the shaft 60 and the connecting bevel gearing, the sector 35 will be pivoted about the pivot pin 36 in manner to move the milling cutter 28 through an arcuate path.

In order that the sector 35 may be turned manually in adjusting the mechanism, the outer end of the shaft 60 is provided with a squared portion 65 for receiving a hand crank. For adjusting the position of the center of the arcuate movement of the cutter 28 relative to the workpiece 30, the main slide 31 may be moved along the ways on the frame 20 by means of a threaded shaft 66 which is journalled in the frame, as shown in Figs. 2 and 3, and that has threaded engagement with a nut 61 formed on and depending from the slide 31, a squared end portion 68 being provided on the shaft 66 for receiving an adjusting crank. The shaft 60 has splined connection with the gear 59 in the gear box 51 to permit sliding movement therebetween when the main slide 31 is moved relative to the frame 20, and clamping bolts are provided for clamping the main slide to the frame in the adjusted position.

IWhen it is desired to move the milling cutter 28 to effect a linear cutting stroke, the gear couplet 58 on the driving shaft 54 is moved to its upper position at the outer end of the shaft by means of a shifting lever 10 (Fig. 1) in manner to mesh with a gear couplet 1| journalled in the gear box 51 concentric with but independently of the shaft 60 and which has meshing engagement with a gear wheel 12 mounted on a shaft 13 journalled in the upper part of the gear box. As shown in Fig. 4, the shaft 13 may be connected by a flexible drive 14, including two universal joints and an intermediate telescoping shaft, to a short shaft 15 that is journalled in a bracket carried by the slide 34 which is mounted on the segment 35. The shaft 15 is provided at its inner end with a bevel pinion 16 that meshes with a bevel pinion 11 on the end of a threaded feed shaft 18 (Fig. 3) that is journalled in the slide 34 and that engages a nut 19 depending from the cutter supporting cradle 33, whereby the cradle and the cutter driving motor 26 carried thereby may be moved transversely of the slide 34.

The feed rate changing and reversing mechanism for regulating the rate and direction of movement of the milling cutter 28 in its feeding stroke is shown diagrammatically in the expanded view, Fig. 5. As there shown, the driving motor 50 is connected to a driving pinion 8| that meshes with a gear Wheel 82 on a main or clutch shaft 83. The main shaft 83 carries a reversing mechanism including a gear wheel 84 mounted on antifriction bearings and that meshes with a gear wheel 85 on a Shaft 86 to constitute a forward feed driving train, and the shaft 83 also carries a rotatably mounted gear wheel 81 meshing with an idler pinion B8 that in turn meshes with a gear wheel 89 on the shaft 86 to constitute a reverse driving train for driving the shaft 86 in the opposite direction. Shaft 86 extends into a feed rate change gear compartment accessible by opening a door 90. The feed changing gearing consists of a pick-off gear 9| removably mounted on the end of the shaft 86 and a complementary pick-ofi gear 92 mounted on the end of a jack shaft 93. The pick-off gears 9| and 92 may be of any selected ratio to transmit power at the desired rate from the shaft 86 to the shaft 93, there being a pinion 94 on the shaft 93 which engages a gear wheel 95 on the main driving shaft 52.

To provide for selecting the direction in which the cutter 28 is moved and for reversing the movement of the cutter at the end of a cutting stroke, the gear wheels 84 and 81 rotatably mounted on the main shaft 83 are arranged to be selectively connected to the shaft 83 by friction clutches 96 and 91 respectively. The friction clutches 96 and 91 are arranged to be engaged alternatively, to operate the cutter driving mechanism in the one or the other direction, by means of a fluid pressure actuated device best shown in Fig. 9 and including a piston element |03 that is slidably mounted on the shaft 83 between the clutches and arranged to be normally urged to a central position therebetween by means of a spring pressed detent mechanism |04. To engage the clutch 96 for driving the mechanism in forward feed direction, fluid pressure is admitted to a chamber |05 at the right end of the piston |03 through a passageway |06 that extends longitudinally of the shaft 83 to the right end thereof, the fluid pressure serving to move the piston |03to the left, as seen in Fig. 9, and to force the plates of the clutch 96 into engagement. To engage the clutch 91 for driving the mechanism in reverse direction, fluid pressure is admitted to a chamber |01 at the left side of the piston |03 through a passageway |08 extending longitudinally of the shaft 83 to the left end thereof. By reason of the fact that the piston |03 acts directly on the plates of the clutches 96 and 91 under the infiuence of the fluid pressure, the apparatus is self-adjusting to compensate for any wear to which the clutch plates may be subjected. When pressure is relieved from both the chamber |05 and the chamber |01, the reaction of the engaged clutch and the pressure of the detent spring forcing the detent mechanism |84 into spherical detent notches in the piston |03, returns the piston |03 to the central position in which position both of the clutches are disengaged.

The driving mechanism for rotating the cutter supporting spindle 21 comprises a worm |20 secured on the shaft of the motor 26 and that meshes with a worm wheel |2| fixed with the spindle 21., as shown in Fig. 3. The worm wheel |2| is provided with a relatively long sleeve |22 encircling the spindle 21 and constituting a reenforcing member for stiffening the spindle. The spindle 21 is rotatably supported within a tapered housing |23 that is attached to and constitutes part of the frame supporting the motor 26 and moves therewith as a unit in pivoting about the pivotal supporting pin 32.

In order that the two spindles of the milling machine may operate close together in performing certain milling operations, the housing |23 of each spindle is made in a shape tapering toward the cutter supporting end of the spindle. As near as possible to the cutter receiving end of each spindle, there is provided an anti-friction bearing |24 comprising an outer race |25 mounted in the tapered end of the housing and an inner race |26 formed integrally with the spindle, together with cooperating anti-friction rollers |21 disposed between the outer and the inner races. By forming the inner race integrally with thel spindle, the diameter of the bearing |24 is reduced to the minimum and it is possible to place it nearer to the cutter receiving end of the spindle than would be the case if the inner race were formed separately and tted over the spindle. The spindle 21 is supported at its other end by an anti-friction bearing |28 carried in a cap |29 tted in the other end of the housing |23. The

cutter receiving end of the spindle is of tapered external contour and is provided with a tapered shield |30 protecting the bearing and with a cylindrical cutter shank receiving socket 3| for receiving the cutter 28. The shank of the cutter 28 is provided with a nat side |32 that engages a driving key |33 in the spindle to prevent rotation of the cutter relative to the spindle. Two set screws |34 and |35 are provided in the spindle for engaging'the dat surface |32 of the cutter shank to retain the cutter in the socket |3| at any desired position longitudinally thereof.

To provide for positioning the cutter 28 longitudinally relative to the spindle 21 in eecting adjustment of the mechanism for performing a predetermined milling operation or to compensate for change in the length of the cutter resulting from sharpening it, there is provided a positioning rod |31 (see Fig. 3) extending longitudinally through a central bore of the spindle 21 and arranged to engage with its forward end the inner end of the cutter shank. The rod I 31 has threaded engagement with the other end of the spindle in such manner that rotation of the rod relative to the spindle results in adjusting the cutter 28 longitudinally of the spindle. For indicating the amount of movement of the cutter relative to the spindle, the adjusting rod |31 is provided at its outer end with a cylindrical indicating dial |38 having graduations disposed to cooperate with an indicating pointer |39 on a cylindrical member |40 in such manner that the cutter may be moved either inwardly or outwardly by a predetermined increment. The cylindrical member |40 is mounted to rotate with the spindle 21 and is associated with an adjusting nut having threaded engagement with the spindle and rotatable thereon for adjusting the spindle bearings. After the cutter 28 has been adjusted, it may be locked in position by tightening the set screws |34 and |35 and the positioning rod |31 may be locked in position by means of a locking mechanism |4| in the exposed end thereof, as more fully shown in the previously mentioned Patent No. 2,227,620.

For positioning the cutter 28 angularly to adapt it for engaging a workpiece, the cutter driving unit may be pivoted about the pivotal supporting pin 32 by means of a pinion |45 that is disposed to mesh with a gear segment |46 formed on the lower arcuate edge of the frame or housing supporting the motor 26 and the spindle 21. As shown in Fig. 6, the pinion |45 is carried on one end of a shaft |41 that is journalled in the supporting cradle 33 and is provided with a squared end |48 for receiving an adjusting crank. After the cutter spindle has been adjusted to the desired inclination, it may be clamped in position by tightening bolts |49 to clamp the frame to the pivot pin 32 and by tightening bolts which engage in an arcuate T slot |50 at the back of the motor frame.

Further adjustment of the position of the cutter 28 relative to the workpiece or to the center of the pivot pin 36 may be accomplished by moving the supporting bracket 33 relative to the slide 34 by means of an adjusting crank applied to a squared end of the threaded shaft 18 shown in Figs. 2 and 3 and the slide 34 may be adjusted in a direction at right angles to the shaft 18 by means of a threaded shaft |52 shown in Fig. l, that is journalled in a bracket carried by the slide 34 and has threaded engagement with a nut |53 mounted on the pivoted sector 35, the shaft |52 having a squared end |54 for receiving an adjusting crank. Clamping bolts are provided for clamping the bracket 33 to the slide 34 and other clamping bolts clamp the slide 34 to the arcuate sector 35. To machine an arcuate contour on a workpiece, the cutter 28 is set at a proper angle to engage the work and at the proper distance from the pivot axis of the sector 35 by the various adjustments just explained, and the pivotal axis is adjusted relative to the workpiece by moving the main slide 31 as previously explained.

The work supporting fixture 23 is mounted at the front of the machine as shown in Fig. 2, and may be adjusted vertically relative thereto by means of a screw and nut elevating mechanism |60 to position the workpiece 30 in proper relation to the pivotal axes of the cutter heads 2| and 22 to effect the desired machining operation.

As best shown in Figs. 2 and 7, the work supporting element 23 comprises a knee portion |63 that is slidably mounted in vertical ways |64 disposed on the front of the main frame 20, and that may be clamped rigidly thereto in the usual manner in the position to which it is adjusted by the elevating mechanism |60. Pivotally mounted upon the knee |63 for movement about a vertical axis is a work supporting head or saddle |65 that is arranged to be turned from the operating position shown in Fig. 2 through ninety degrees in counter-clockwise direction to a loading position. Pivotal movement of the head 65 is effected by means of a piston |66 shown in Figs. 7 and 9 that operates in a cylinder |61 mounted on the knee |63. The piston |66 is attached to a piston rod |68 provided with rack teeth |69 that mesh with a pinion |10 secured to a depending hub portion 1| of the head |65 that is journalled in the knee |63 by an anti-friction bearing |12. Movement of the pivoting head |65 to the operating position is limited by a positive stop |15 (Fig. 2) on the knee which engages the head and accurately positions it to support the workpiece in alignment with the cutters. Another similar positive stop |16 is provided at the other side of the knee for stopping the head in the loading position. After the head has been pivoted to the operating position, it may be rigidly clamped by means of a circular clamp |11 that engages a gib |18 on the hub I 1| of the head and that is actuated by a clamping lever |19 at the left side of the knee.

The pivotally mounted head |65 supports a work holding fixture that is slidably mounted thereon for linear movement toward or from the cutters. As shown in Fig. 7, the xture |80 has connected to it a piston rod |8| carrying a piston |82 that operates within a cylinder |83 formed in the rotatable head |65. Sliding movement of t-he fixture |80 is effected by admitting fluid under pressure to the cylinder |83 at one or the other side of the piston |82,

The forward nose portion of the fixture |80 is ararnged to rotatably support a work holder |85 that may be turned about a horizontal axis to position the workpiece for successive cutting operations. As shown in Fig. 7, the workholder |85 is in the form of a sleeve journalled in the xture |80 and is provided with an encircling bevel gear |86 that meshes with a bevel pinion |81 (Fig. 8), carried on an indexing shaft |88 that is journalled in the fixture |80 at right angles to the sleeve and is provided at its outer end with an indexing crank |89, the gear ratio being such that four turns of the crank |89 result in one complete revolution of the work holder |85.

The work holder |85 is provided with two separate clamps for engaging the workpiece 30 at spaced positions, each clamp being independently operated in a manner to exert substantially equal clamping pressures. As shown in Fig. 7, the work clamp comprises a forward split collet |92 that is supported within the forward end of the work holder |85 against a retaining ring |93 in position to engage a cylindrical portion of the workpiece. The second clamp comprises a similar split collet |94 disposed co-axially with and inwardly of the collet |92 in position to engage another cylindrical portion at the inner end of the workpiece. Although the workpiece is shown as presenting cylindrical surfaces for engagement by the collets |92 and |94, it will be understood that collets of other than cylindrical shape and of other sizes may be substituted for gripping a workpiece of different shape. The two collets |92 and |94 are arranged in abutting relationship and the inner collet is engaged by a retaining ring |95 that is supported from the work holding sleeve |85 by means of pins |96 in such manner as to hold the collets against each other and against the retaining ring |93 to prevent endwise movement thereof.

As shown, bothof the collets |92 and |94 are provided with tapered external surfaces for engagement by complementary actuating sleeves |98 and |99 respectively, the sleeve |99 being positioned within the sleeve 98. The sleeves 98 and |99 are also split longitudinally to provide for circumferential resilience and they are so arranged that upon movement toward the forward end of the work holder, they coact with the tapered surfaces of the cooperating collets |92 and |94 and cause them to contract and grip the workpiece. The actuating sleeve |98 is arranged to be operated by a cylindrical sleeve 20| which is operatively connected to it by an anti-friction thrust bearing 202 constituting a swivelling connection permitting the sleeve |98 to turn with the work holder |85 during indexing operations while the sleeve 20| remains stationary within the body of the fixture |80. For moving the sleeve 20| longitudinally to effect clamping action of the collet |92, there is provided a piston 203 which is attached to the end of the sleeve in position to operate within a cylinder 204 attached to the back of the xture |80 in co-axial relationship with the clamping collets. For moving the inner actuating sleeve |99 there is provided a cylindrical sleeve 201 arranged to operate within the sleeve 20| and having swivelling operative connection with the actuating sleeve |99 by means of an anti-friction thrust bearing 208. The sleeve 201 is also provided with a piston 209 which is arranged to slide within a cylindrical inner surface of the piston 203, the arrangement being such that when the fluid pressure is applied to the back of the piston in the outer end of the cylinder 204, both the piston 203 and the piston 209 will be moved forward independently of each other to apply independent clamping action upon the two portions of the workpiece by the collets |92 and |94.

For positioning the workpiece 30 in the work holder, there is provided a positioning fixture or gauge 2 I5 that is pivotally supported on a bar 2 6 adjustably mounted on the top of the work holding xture |80 in such manner that it may be swung down into work-engaging position as shown in Fig. 7 or turned upward to an inactive position as shown in Figs. 1 and 2. When the xture 2|5 is in the position shown in Fig. '1, it is adapted to engage the end of a workpiece 30 by means of a plain stop surface 2|1 extending transversely of the axis of the workpiece and to engage a locating side of the workpiece by means of a transversely adjustable member 2|8 having a flat positioning surface extending parallel with the axis of the workpiece. The workpiece 30 is urged against the positioning fixture 2I5 by means of a springloaded positioning bar 2|9 that extends longitudinally through the inner operating sleeve 201 and is urged in forward direction by means of a spring 222. After the workpiece has been positioned in the workholder by the positioning fixture 2|5, the clamping collets |92 and |94 are contracted to grip the workpiece by admitting fluid pressure to the right end of the cylinder 204 and the positioning xture is then swung up to its inactive position.

Fluid pressure for actuating the clamping pistons and for operating the other iiuid actuated parts of the machine is provided by a pump 225 that is directly connected to the end of the shaft of the driving motor 50, as shown in Fig. 5, for operation thereby to withdraw liquid from a sump 226 in the bottom of the main frame 20 by means of a suction pipe 221. Referring to the circuit diagram in Fig. 9, liquid under pressure from the pump 225 passes through a conduit 228 into a pressure relief valve 229, which serves to limit the pressure in the conduit to a predetermined maximum and to permit any excess liquid to iiow through a conduit 230 into a return conduit 23| which leads back to the sump 226. From the relief valve 22S, the pressure liquid passes through a conduit 232 into a by-pass valve 233, from which it flows through a conduit 234 to a work-clamping valve 235. To clamp the workpiece, a clamping lever 236 on the valve 235 is moved from the position shown in dotted lines to the solid line position, thereby admitting fluid from the valve 235 through the conduit 231 into the right end of the cylinder 204 to exert clamping pressure upon both the piston 203 and the piston 209 to move them forward and contract the collets |92 and |94. Fluid in the forward end of the cylinder 204 flows outward through a conduit 238 into the valve 235 and thence into the return conduit 23|.

After the workpiece has been clamped in the workholder, the pivotally mounted supporting head is turned in clockwise direction to operating position. For this purpose, liquid under pressure flows from the by-pass valve 233 which functions to permit the liquid to pass into a conduit 24| from which a branch line 242 leads to a control valve 243, the arrangement being such that should the pressure in the system drop below a predetermined minimum the by-pass valve 233 will close the conduit 24| to conserve the remaining liquid pressure for action on the work clamping mechanism. The valve 243 controls the swinging or pivoting movement of the work-holding head |65 and it is actuated by a cam plate 244 which may be turned by an operating lever 245, shown in Fig. 9 to any one of three positions, a detent mechanism 246 (Fig. 11) being provided to retain the cam in the selected position. The cam plate 244 is provided with a cam groove 241 that engages a cam follower 248 on the operating stem of the valve 243. The shape of the cam groove 241 is such that when the operating lever 245 is moved from the position A shown in dotted lines to the dotted line position B, the valve 243 will be positioned to admit pressure fluid through a conduit 250 to the inner or left end of the cylinder |61, thereby forcing the piston |66 to the right and turning the worksupporting head |65 clockwise from the loading position to the operating position. Fluid in the outer or right end of the cylinder |61 escapes through a series of exhaust openings 25| into an exhaust passageway 252 and thence through the valve 243 to a conduit 253 that connects to the return conduit 23|. As the pivoting headl |65 approaches the working position and the piston |66 approaches the right end of the cylinder |61, the exhaust passageways 25| are successively closed by the piston as shown in Fi-g. 9, thereby reducing the rate of flow of the liquid and checking the movement of the swinging head. After the last one of the exhaust openings 25| is closed by the piston |66, the remaining iiuid in the end of the cylinder |61 escapes through an auxiliary passageway 254 having a constricted portion 255 of such limited capacity that the final movement of the work-supporting head into working position occurs very slowly in order that the head may engage the positive positioning stop -without shock. After the work supporting head |65 has been turned to working position, it is clamped `by actuating the clamping lever |19 to engage the circular clamp |11 with the gib |18 on the hub |1| of the head, thereby drawing the head down tightly upon the top of the knee |63.

To advance the workpiece to the cutters the operating lever 245 may then -be moved from position B to position C, the shape of the cam groove 241 being s-uch that no change occurs in the position of the valve 243. In moving the lever from position B to position C, a second cam groove 256 in the cam plate 244 acts upon a cam follower 251 on the stem of a control valve 258 in manner to position the valve for admitting pressure fluid, owing to it from the conduit 24| through a branch conduit 259, into a conduit 268 that leads to the right end of the cylinder |83 to move the work-holding fixture |88 forward toward the cutters. As the uid is admitted into the right end of the cylinder |83, it forces the piston |82 to the left and the fluid in the left end of the cylinder escapes through a rapid traverse rate passageway 26| and a feed rate passageway 262, both of which lead to an exhaust conduit 263 through which the exhaust fiuid returns to the valve 258 and thence through a conduit 264 to the conduit 253 and the return conduit 23| leading to the sump 226. Both the pressure conduit 268 and the exhaust conduit 263 pass through a cylindrical plug 265 that is mounted in the center of the hub |1| and that constitutes a rotatable connection with the swinging head |65.

The arrangement is such that the fluid pressure acting on the right end of the piston |82 causes the workpiece 38 to advance toward the cutters 28 at rapid traverse rate. As the workpiece approaches the cutters, an adjustable actuating rod 218 carried by a bracket 21| that is mounted on the piston rod I8|, moves into contact with a cut-off valve 212, which is slidably mounted in the fixture in cooperating relationship with the rapid traverse passageway 26|, and is held in retracted position by a spring 213, the rod moving the valve forward to close off the passageway, as shown in Fig. 9. After the passageway 26| is closed, all of the escaping exhaust duid from the cylinder |83 must pass through the feed rate passageway 262 which is provided with an adjustable throttle valve 214 .by means of which the rate of flow of the exhaust uid may be regulated in order that the workpiece 38 may be fed against the cutters at a predetermined rate to permit the cutters to feed into the cavities of the workpiece along a linear path. To position the cutters accurately within the workpiece at the point from which the arcuate cutting stroke is to start, the bracket 21| on the piston rod I8| is provided with an adjustable positive stop sleeve 216 which is disposed concentric with the rod 210 and may be set to abut a stop member 211 on the head |65 when the workpiece arrives at the predetermined position.

After the forward feeding movement of the work-holding fixture |88 has been completed, the xture is clamped to the head |65 by actuating a clamping lever 218 (Fig. 2) to support the workpiece rigidly in position for the feeding or cutting stroke of the cutters 28.

To initiate the cutting stroke, a starting lever 28| associated with a direction controlling valve 282 as shown in Fig. 9, is actuated to move a plunger 283 of the valve to its upper position. With the valve plunger 263 in its upper position, pressure fluid from the pump 225 is permitted to flow by way of the conduit 228, relief valve 229 and conduit 232, through a conduit 284 and a passageway 285 in the body of the valve 282 to a port 286 and thence through a groove 281 in the valve plunger 283 to a port 288, which is connected by a conduit 289 to the passageway |86 in the right end of the driving shaft 83. As previously explained, when pressure fluid is admitted to the passageway |86, it flows into the chamber and forces the piston |83 to the left, thereby engaging the forward driving friction clutch 96 to cause the transmission mechanism 5| to swing the cutting heads 2| and 22 in the forward cutter feeding direction.

During the forward cutting stroke, the cutters 28 each take a roughing cut on the workpiece 28 along an arcuate path. As the cutting stroke progresses, a control drum 298, mounted at the rear of the machine, as shown in Fig. 1, is rotated in clockwise direction, as seen in Fig. 9, by a shaft 29| that is driven by a worm wheel 292 meshing with a worm 293 on the main driving shaft 52 as shown in Fig. 5. At the end of the cutting stroke a reversing trip dog 295 on the drum 298 engages a pivotally mounted trip lever 296 having an arm 291 that engages a plunger 298 of a. re-

- versing pilot valve 299, the arrangement being such that when the trip dog 295 moves the trip lever 296 to the right, the plunger 298 is moved upwardly against the resistance of a spring 388 to a position in which a groove 38| on the plunger communicates with a port `382 in the valve body which is connected with the pressure fluid passageway 285. Pressure fluid from the port 382 then flows along the groove 38| to a port 383 connected by a passageway 384 to a chamber 385 encircling the directional valve plunger 283. Pressure in the chamber 385 forces the valve plunger 283 downward below the position in which it is shown in Fig. 9, thereby moving a land 386 of the plunger 283 past the port 286 to cut off the ow of pressure fluid to the port 288 and to permit flow thereof through a groove 381 to a port 388 which is connected by a conduit 389 to the passageway |88 in the left end of the shaft 83. Fluid under pressure from the conduit 389 passes through the passageway |88 into the chamber |81 and forces the piston |83 to the right thereby disengaging the forward feed driving clutch 96 and engaging the reverse driving clutch 91, the fluid in the chamber |85 being forced out through the passageway |86, the conduit 289 and valve port 288, to the groove 281 which now connects with an exhaust port 3|8 communicating with an exhaust conduit 3|| which is connected to the return conduit 23|. Upon engagement of the reverse clutch 91, the

passageway 304, the port 303, the groove 30|,

port 3|2, and a conduit 3|3 which connects with the return conduit 23|, thereby releasing the directional control valve plunger 283 for movement manually by the lever 28| should it be desired to stop the feeding movement. As the cutters 28 return through the finishing cut to their starting positions, the control drum 290 is turned in counter-clockwise direction until a stop dog 320 on the drum moves into engagement with the trip lever 296. When the stop dog 320 engages the trip lever 296 and moves it to the left, an arm 32| of the lever 296 engages the lower end of the directional control valve plunger 283 and moves it upward to the neutral position shown in Fig. 9, a detent mechanism 322 being provided for retaining the valve plunger in either its central neutral position or its upper forward cutter feed ldriving position. As may be seen in Fig. l, the stop dog 320 is provided with an adjusting screw 323 for accurately and rigidly positioning it.

When the valve plunger 283 is in the neutral position as shown in Fig. 9, the pressure port 286 is closed by the land 306, thereby cutting oif the supply of pressure fluid to the reversing clutch mechanism, and the groove 281 communicates with the exhaust port 3|0 to permit exhaust liquid from the chamber of the reversing mechanism to fiow through the passageway |06,

, the conduit 289 and port y288, into the exhaust conduit 3| Also the groove 301 communicates with an exhaust port 325 to permit exhaust iiuid from the chamber |01 to flow through the passageway |08, the conduit 309 and port 308 through the port 325 into an exhaust conduit 326 which connects with the exhaust conduit 3| I. This results in relieving pressure from both sides of the clutch actuating piston |03 and in permitting the piston to move to its central neutral position under the iniiuence of the detent mechanism |04 thereby stopping the feeding movement of the cutter carrying heads.

After the finishing cut movement of the cutters has been terminated, the workpiece may be withdrawn from the cutters for the purpose of indexing it to a new position for a second cut. To insure that the workpiece will not be moved while the cutters are moving through the cutting stroke, a mechanical interlocking arrangement is provided, as shown diagrammatically in Fig. 9, and in detail in Figs. l0 and 11. To this end, the feed starting lever 28| is pivotally connected by a link 330 to an interlocking plunger or control bar 33| that is associated with the control lever 245, the arrangement being such that When the feeding lever 28| is in the neutral position, the interlocking plunger is so placed that the control lever 245 may be moved to any of its three positions. As shown in Figs. and 11, the interlocking plunger 33| is provided with a notch 332 which is positioned to permit a lug 333 on the lever 245 to pass through it in turning the cam plate 244 from one position to another, the control bar 33| preventing movement of the lever 245 when the notch 332 is not in alignment with the lug 333. This interlocking mechanism prevents starting the cutting heads through a cutting stroke when the work-holding fixture is not in operating position inasmuch as under these conditions the lug 333 of the lever 245 then engages the notch 332 and prevents movement of the starting lever 28|.

To withdraw the workpiece from the cutters, the Workholding fixture is rst unclamped by actuating the clamping lever 218 and then the control lever 245 is moved from position C to position B, thereby admitting uid under pressure from the pump 225 through the control valve 258 and the conduit 263 to the passage 262 leading to the left end of the cylinder |83, causing the piston |82 to move to the right. The workpiece 30 may then be indexed to its new position, in this instance by turning it through one hundred and eighty degrees, to present the other side thereof (as may be seen in Fig. 1) to the cutters. The one hundred and eighty degree indexing movement is accomplished by turning the indexing crank |89 through two complete revolutions and then reengaging a spring pressed pin 335 on the crank in a socket 336 in the body of the fixture |80, as shown in Fig. 8. Turning the crank |89 results in rotating the work-carrying sleeve within the front of the work-holding fixture and with it the clamping collets |92 and |94, together with their actuating sleeves, the rotation of the sleeves being permitted by the swivelling connections afforded by the anti-friction bearings 202 and 208. After the workpiece has been indexed, it is clamped in the new position by actuating a clamping lever 340 after which the work-holding fixture |80 may be moved forward to engage the work with the cutters a second time, by moving the control lever 245 from the position B to the position C, as previously explained. The fixture is then clamped by means of the lever 218 and the second cutting stroke is started by means of the starting lever 28|, the mechanical interlock being so arranged that with the lever 245 at position C, the lug 333 is disengaged from the notch 332.

After the second cut has been completed and the directional valve 283 and its lever 28| have been returned to stop position, the notch 332 is again brought into alignment with the lug 333 to permit movement of the control lever 245. The clamp lever 218 is then operated to unclamp the sliding fixture |80 and the control lever 245 is moved from position C to position B to effect retraction of the workpiece from the cutters, as previously explained. In this operation, the cam disc 244 acts as an interlock to prevent turning movement of the work-holding head |65 while the control lever 245 is in position B to avoid swinging the workpiece sidewise against one of the cutters. After the workpiece has been retracted, the work supporting head |65 is unclamped by releasing the circular clamp |11 from the gib |18 by actuating the clamping lever |19, and the control lever 245 is then moved from position B to position A to position the control valve 243 for admitting pressure fluid through the conduit 252 to the right end of the cylinder |61, thereby forcing the piston |66 to the left and turning the work head counterclockwise to the unloading position. Liquid in the left end of the cylinder |61 escapes through a series of exhaust openings 35|, which are successively closed by the piston to decelerate the movement, the final movement occurring at slow rate by the escape of liquid through an auxiliary exhaust passage 355 having a constricted portion 356.

After the work-supporting head |65 has been pivoted to the unloading position, the workclamping lever 236 is actuated to unclamp the workpiece 30 by positioning the Valve 235 in a manner to admit pressure fluid through the conduit 238 to the left end of the cylinder 204. The fluid pressure in the left end of the cylinder urges the piston 203 to the right and also exerts pressure on the piston 209 independently by reason of the fluid passing through passageways 360 in the piston 203 to act upon the face of the piston 209. Movement of the pistons 203 and 209 to the right, as seen in Figs. 7 and 9, withdraws the actuating sleeves |98 and |99 from the tapered outer surfaces of the clamping collets |92 and |94 and permits the collets to expand and release the workpiece 30. 'Ihe pistons 203 and 209 are interconnected by an interlocking lost motion mechanism in such manner as to permit independent clamping action thereof and to provide for cooperative unclamping action. Should either one of the actuating sleeves |98 or |99 resist the unclamping action of its associated piston, the lost motion of the mechanism is taken up by movement of the other piston, and the force exerted by the pressure fluid uponthe full area of both pistons is then applied to release the resisting clamp. For instance, should the inner clamping sleeve |99 resist movement, the outer piston 203 in moving to the right would strike against the inner piston 209 exerting a blow or force upon it tending to assist in the unclamping action. If the outer clamping sleeve |98 resists, the inner piston 209 in moving to the right engages a retaining ring 36| in the inner surface of the piston 203 and exerts force thereon to assist in the unclamping action. After the collets |92 and |94 have released the workpiece 30, it may be removed from the work-holding fixture. Any chips or coolant liquid that may drop from the finished workpiece at the loading position are caught in a trough which communicates with the main chip receiving trough at the center of the frame 20. Another workpiece may then be inserted in the workholder and clamped therein by actuating the clamping lever 236 and the cycle of operations just described may then be repeated.

A modified form of milling machine embodying the invention is shown in Figs. l2 to 15 inclusive of the drawings. The apparatus there disclosed, while generally similar to that shown in the previously described form of the invention, comprises a machine embodying improved structural and control features that combine to produce a simplified machine capable of performing the desired operation of accurately milling ball raceways at an increased rate of production. The structural improvements include a simplified cutter supporting mechanism that is designed to provide the same flexibility in the adjustment and movements of the cutter heads obtainable in the other form of the invention with the elimination of the main or base slide. A further improvement disclosed in the modified form of the invention resides in the application of adjustable reversing and stop clogs to the rotatably mounted cutter supporting table to provide improved means for adjusting and accurately controlling the feeding and retracting movements imparted to the milling cutters. An improved transmission mechanism is disclosed including means adjustable to selectively effect the return stroke of the cutters at either a feed or rapid traverse rate of movement. A further improvement includes the provision of valve means in the hydraulic circuit for effecting the more rapid return stroke of the work holder upon completion of the cutting action of the tool in the workpiece. In accordance with the production requirements of a machine of the character of the present invention the modified form of the milling machine shown has been further simplified by the elimination of the knee that provided means for adjusting the ele- Vation of the workpiece, the adjustments afforded the tool being ample to satisfy the requirements. The means for effecting straight line power feed ing movement to the cutters has also been eliminated in the modified form of the present invention since this movement is required only on special work other than that for which the present machine is particularly adapted.

Referring specifically to the drawings, and more particularly to Figs. 12 and 13 thereof, the modified form of the milling machine comprises a bed 400 having at each side thereof an inwardly inclined surface 40| on which a bed plate 402 is iixedly mounted to serve as a support for cutter receiving and driving mechanisms or heads 42| and 422 respectively disposed to cooperate with a Work lsup-porting element 423 mounted for indexable movement on a top front horizontal surface 403 of the bed 400.

As may best be seen in Fig. 12, each of the cutter heads 42| and 422 includes a driving motor 426 operatively connected to drive a tool spindle 21 constructed and driven in the manner previously described. Each driving motor 426 and tool spindle 21 is secured to `a base 433 that is slidably mounted for movement, to adjust the position of the milling cutters 28, with respect to the workpiece 30, upon ways formed in a sliding plate 434 that is mounted for movement upon ways formed in a rotatably mounted table 435 and disposed at right angles to the ways formed in the sliding plate 434. Each table 435 is supported on the inclined surface of the adjacent bed plate 402 and is provided with a hub portion 436 that is journalled for rotation in a suitable bearing 404 formed in the bed plate 402. The rotatable table 435 is retained on the bed plate 402 by a securing ring 405 applied to the lower end of the hub portion 436 thereof.

Movement of either of the cutters 28 to mill a surface of arcuate contour is accomplished by rotating the table 435 on the bed plate 402 and the position and degree of curvature of the arcuate surface 'is determined by the position of adjustment of the cutter supporting base 433 on the sliding plate 434, the position of adjustment of the sliding plate 434 on the rotary table 435 and the amount of rotary movement afforded the table 435` After the several elements have been properly adjusted they are clamped in desired position in the usual manner.

The power driving mechanism for moving the cutter supporting heads 42| and 422 through the cutting stroke, comprises essentially a driving motor 440 that is mounted on a gear box 44l, containing feed rate changing and reversing mechanism 442, the box being secured to the right hand end of the bed 420 (as shown in Fig. l2). The armature shaft of the motor extends into the gear box 44| and is provided with a worm 443 adapted to mesh with and drive a worm wheel 444 (see Fig. 14) secured to a jack shaft 445 journalled 'in the gear box 44|, The

rotation of the shaft 419.

jack sh-aft 445 also has spur gears 446 and 441 secured thereto. The spur gear 446 serves to provide a power take off for the feed rate of movement while the spur gear 441 serves to provide a power take off for rapid traverse movement. The spur gear 446 meshes with and drives a spur gear 448 'secured to a counter shaft 449 also journalled for rotation in the gear box 44|. The outer end of the shaft 449 terminates in a splined end disposed in a pick-off gear chamber 459 that is accessible by opening a hinged door 45|. Another counter shaft 452 arranged parallel with the shaft 449 is journalled in the gear box 44| and is provided with a splined end disposed in the Ipick-off gear chamber 459. 'I'he feed changing gearing consists of pick-off gears 453 and 454 removably mounted on the splined ends respectively of shafts 449 and 452. The pick-off gears 453 and 454 may be of any selected ratio to transmit driving power at the desired rate from the shaft 449 to the shaft 452. The shaft 452 also has spur gears 455 and 456 secured thereto, these gears serve respectively to drive the direction reversing mechanism in forward or reverse direction.

To provide for selecting the direction in which the cutter 28 is to be moved and for reversing the direction of movement of the cutter at the end of a cutting stroke, the spur gears 455 and 456 are arranged to be selectively connected respectively to a shaft 451 that carries direction selecting friction clutches 96 and 91 identical in con.. struction and operation with those previously described in connection with the other form of the invention shown in the accompanying drawings. The clutches 96 and 91 are arranged to be engaged selectively in the manner previously described to operate the cutter driving mechanism in one or the other direction. The clutch 96 serving when engaged to effect the forward movement of the cutter 28 into the workpiece and the clutch 91 serving when engaged to effect the retracting movement of the cutter. One element of the clutch 96 carries a gear 458 that meshes directly with the gear 455 on the shaft 452 to form a connection for driving the mechanism at feed rate in a forward direction. The gear 456 may be connected to a gear 459 on one element of the clutch 91 through a sliding idler gear 469 that may be shifted into meshing engagement with the gears 456 and 459 to provide a connection for driving the mechanism at feed rate in the reverse direction. A bevel gear 46| secured to the shaft 451 meshes with and drives a mating bevel gear 462 secured to a drive shaft 463, The shaft 463 is provided with a safety clutch mechanism 464, shown in Fig. 12, that is operative upon overload to slip to preclude the possibility of damage to the transmission or other parts of the machine.

The means for effecting manual rotary movement of the tables 435 to provide proper angular adjustment thereof for the purpose of setting up the machine prior to the application of driving power is similar for each of the cutter heads 42| and 422, except for being oppositely arranged, the mechanism for the right head 42| only being shown in detail in Fig. 12 as illustrative of the structure.

' As shown in Fig. 12, the manually operable table adjusting means includes a shaft 419, arranged parallel with the plate 402, that is journalled in the bed 499 and provided at its outer exposed end with a squared portion 41| adapted to receive a hand crank for effecting manual A spur gear 412 secured to the shaft 410 meshes with and drives a mating spur gear 413 secured on a jack shaft 414, journalled in the bed plate 402, that is also provided with a worm 415 adapted to mesh with and drive a worm wheel 416 in the form of a ring that is pressed on and secured to the lower portion of the rotatably mounted table 435. The rotatable tables 435 are provided with graduations 411 disposed about their circumference to be read against a pointer (not shown) to facilitate accurate and identical angular positioning of the rotary tables 435 with respect to the workpiece 30.

The power driving mechanism for effecting movement of the table 435 to move the cutter supporting head 42| through a cutting stroke is derived from the main drive shaft 463 which may be coupled with the shaft 410 by shifting a clutch element 480, that has a splined connection with the shaft 419 and is provided with clutch lteeth adapted to engage complementary teeth formed on the hub of a bevel gear 48| that meshes with a mating bevel gear 482 secured to the main drive shaft 463. The means for selectively engaging the clutch element 480 consists of a manually operable lever 483 that is moved from the position shown in Fig. 12 to its other extreme position wherein it effects the establishment of a driving connection between the shaft 463 and the shaft 419 to effect power movement of the rotary table. Identical means oppositely arranged is provided for establishing a driving connection for the cutter supporting head 422.

The means for controlling the extent of move ment of the rotary table 435 under power consists of a pair of trip dogs 485 and 486 (Fig. 15) adapted for adjustable positioning in an annular T-slot 481 formed in the outer. surface of the right hand rotary table 435 (as shown in Fig. 12). After the starting position for the cutting stroke has been set up by manual adjustment of the several elements of the cutter supporting heads 42| and 422, the trip dog 485 may be adjusted to the proper position in the slot 481 and clamped therein to limit the movement of the tables in one direction by its action upon the valve plunger 283 of the direction controlling valve 282, the valve 282 functioning in a manner identical to that described in connection with the previously described form of the invention. The trip dog 486 may then `be adjusted in the slot 481 and clamped therein to set the amount of rotation in the other direction permitted the rotary tables 435. The trip dog 486 acts upon the valve plunger 298 of the reversing valve 299 to effect a reversal in the direction of table rotation in a manner identical with that previously described.

The manual means for effecting movement of the direction valve 282 comprises the lever 28| that transmits movement to the valve plunger 283 through a pair of bevel gears 488 (Fig. 13) secured to the shaft carrying the lever 28| and a control shaft that is also provided with a means at its upper extremity operative to eiect movement of an arm 499 that is connected with the valve plunger 283 to shift it upon manual operation of the control lever 28|.

The improved transmission disclosed in the modified form of the invention includes manually operable means for selecting the speed of return movement of the cutters 28 at either feed or rapid traverse rate. The means for accomplishing the rate selection of return movement of the cutters 28 comprises the sliclable mounting forl the idler gear 460. Referring to Fig. 14, it will be noted that the gear 459 forming a part of the clutch 91 is of sufficient Width to include both the feed rate driving gear 456 carried by the shaft 452 and the axially aligned rapid traverse rate driving gear 441 carried by the shaft 445. As the result of this arrangement, the idler gear 460, that is slidably mounted on a stub shaft 490 and in constant mesh with the gear 459, may be shifted laterally to selectively engage either the feed rate gear 456 or the rapid traverse rate gear 441. The manually operable mean-s for effecting the rate selection comprises a selector knob 49| (see Fig. 13) that may be shifted from one end of a slot 492 formed in the side of the gear box 44| to the other end of the slot. The knob 49| is threaded onto the outer end of a stud 493 (see Fig. 14) that is anchored in a rod 494 that is slidably mounted for axial movement in the box 44|. A shifter fork 495 secured to the rod 494 engages a groove formed in the hub of the idler gear 460 so that the gear 460 is slid along the face of the gear 459 upon axial movement of the rod 494. The rate selection mechanism may be shifted from the rapid traverse rate position shown in Figs. 13 and 14 to feed rate by unscrewing the knob 49| a sufficient amount to free the hub thereof from contact with the enlarged opening formed at the end of the slot 492, the knob may then be moved from the extreme right to the extreme left position (referring to Fig. 13) thus effecting movement of the gear 460 out of mesh with the rapid traverse gear 441 and into mesh with the feed rate gear 456. When this shift has been accomplished, the knob may be turned to effect the advance of its hub portion into the enlarged opening formed at the left end of the slot, to releasably retain the idler gear 460 in mesh with the feed rate gear 456. y

A further improvement in the modified form of the invention resides in the provision of an improved valve means in the hydraulic circuit whereby a more rapid return stroke of the work holder 423 may be effected upon completion of the cutting operation of the tool 28 upon the workpiece 30. The improved valve means is shown in Fig. 9 and comprises the inclusion in the adjustable throttle valve 214 of a check valve 500 operable upon movement of the control valve 258 to reverse position B to effect rapid movement of the work holder 423 on its return stroke. Ihe check valve 500 is mounted in a by-pass passage 50| disposed in parallel relationship with the passage 262 and arranged to bridge the adjustable throttle valve 214. The by-pass passage 50| is enlarged to receive a spring urged ball 502 constituting the valve element that renders the y-pass passage 50| ineffective during the forward movement of the work holding fixture toward the cutters 28 so that the final feeding movement of the workpiece 30 is controlled in the manner previously described. However, the check valve 500 is operable to permit the full force of the fluid under pressure to initiate the return movement of the piston |82 at a rapid traverse rate immediately upon the reversal of the control valve 258, thus eliminating the delay in the cycle of operation that resulted from the necessity of initiating the return stroke of the piston |82 at the same rate of movement as that required at the final portion of its feeding stroke.

As the elements of the machine not specifically referred to in the description of the modified form of the invention are identical in structure and mode of operation -with those described in detail in the portion of the specification referring to the form shown in Figs. 1 to 11 inclusive. of the drawings, it is not deemed necessary to repeat the detailed description of the function and operation of elements common to both forms of the invention.

Although specific forms of the invention have been described in detail in order to disclose clearly the several features of the invention, it is understood that the particular apparatus shown and described are susceptible of various modications that will be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the subioined claims.

We claim:

l. In a milling machine having a frame carrying a rotatable cutter, a work-holding fixture disposed to be rotated from a loading position to an operating position and to be moved lineally while in said operating position to advance a workpiece into engagement with said cutter, and control mechanism operative to effect said rotary and said lineal movements of said workpiece, said control mechanism being arranged to prevent rotary movement of said work holder while it is in advanced position and to prevent advancing movement thereof except when it is turned to its operating position.

2. In a milling machine, the combination with a main frame and a work-supporting xture mounted on said frame, of cutter-supporting apparatus including an oscillatable slide pivotally carried by said frame, a reciprocatable slide carried by said oscillatable slide, and a cutter spindle carried by said reciprocatable slide in cooperating relationship with said work-supporting fixture, together with driving mechanism having reversing and speed changing gearing, and selective gearing disposed to connect said driving mechanism to actuate either said oscillatable slide or said reciprocatable slide alternatively, whereby a cutter carried by said spindle may be moved along either an arcuate path or a linear path.

3. In a machine tool having relatively movable work supporting and cutter supporting elements, means for effecting relative movement of said elements selectively in forward or reverse direction including a pair of alternatively engageable hydraulically actuated forward and reverse friction clutches, a speed changing mechanism operatively connected to drive said friction clutches in manner to effect said relative movement at a predetermined feed rate, and a sliding gear associated with said reverse friction clutch and selectively engageable to drive it at feed rate or at rapid traverse rate, whereby relative movement of said supporting elements in reverse direction may be eifected by said reverse friction clutch either at feed rate or at rapid traverse rate.l

4. In a machine tool having relatively movable work supporting and cutter supporting elements, means for effecting relative movement of Vsaid elements selectively in forward or reverse direction including a pair of alternatively engageable hydraulically actuated forward and reverse friction clutches, means for limiting the movement of said cutter supporting elements in both directions, a speed changing mechanism operatively connected to drive said friction clutchesin manner to effect said relative movement at a predetermined feed rate, and a sliding gear associated with said reverse friction clutch and selectively engageable to drive it at feed rate or at 'rapid 

